This invention relates to methods of operating intermetallic negative electrodes for non-aqueous lithium cells and batteries. More specifically, it relates to methods of operating modified compositions of copper-tin electrodes, Cu6-xMxSn5, wherein xxe2x89xa63 and in which M is one or more metals including silicon, and to methods using current collectors and grain growth inhibitors when used with such electrodes, and to controlled operating conditions for the lithium cells and batteries using such intermetallic electrodes. Preferred compositions useful in the inventive methods include Cu6-xMxSn5 electrodes in which the copper atoms are partially replaced by one or more transition metals and lithium in partial replacement M and Li or one or more of M including Li. Improved electrochemical performance with respect to delivered capacity and cycling stability of the lithium cells over those known in the art is obtained by controlling the structure of the lithiated Cu6-xMxSn5 electrodes and by controlling the voltage of the lithium cell such that the potential of the lithiated intermetallic negative electrode at the top of charge is less than 0.2 V but greater than 0 V vs. metallic lithium.
A significant problem in the field is that copper-tin electrodes, notably Cu6Sn5, lose capacity if cycled repeatedly to 0 V vs. metallic lithium. When cycled to 200 mV vs. lithium, the capacity retention is improved significantly, but at the expense of the delivered amount of capacity.
The invention relates to a method of using intermetallic negative electrodes based on copper-tin, Cu6Sn5, for non-aqueous electrochemical lithium cells and batteries. The invention relates more specifically to the use of modified electrode compositions, Cu6-xMxSn5, wherein xxe2x89xa63 and where M is one or more metals used in the inventive method, preferably a first row transition metal and lithium, that when cycled in an electrochemical cell the voltage of cell is controlled such that the potential of the lithiated intermetallic negative electrode at the top of charge is less than 0.2 V but greater than 0 V vs. metallic lithium. The Cu6-xMxSn5 electrodes optionally contain additional M metal (or metals) in the electrode either in finely divided, dispersed and intimately mixed form or as a substrate to act as current collector. The electrodes may also contain additional components to control porosity and current collection or to suppress grain growth in the electrode during electrochemical operation. Such modifications to the composition of copper-tin electrodes and to the regulation of the operating conditions of the cells improve the capacity and cycle life of lithium cells and batteries. The superior electrochemical performance is achieved by controlling the structure of the lithiated Cu6-xMxSn5 electrodes, either electronically by controlling the voltage of the lithium cell, or by limiting the installed capacity in the positive electrode.